BoilerFaultCodesVaillant P.6 Fault Code
Also written as P6 — same fault.
The Vaillant P.6 fault code means: your boiler is currently running a self-diagnostic test to check the water pressure and fill level as it prepares to start up.. It appears on 8 Vaillant models in our database.
Technical description: Filling test program. The diverter valve moves to the centre position
What causes the Vaillant P.6 fault?
This is a routine diagnostic phase where the boiler verifies there is enough water pressure to operate safely. It occurs when the appliance is first powered on or after a periods of inactivity, as the system checks that the internal valves are in the correct position. It is a sign the boiler is performing its internal safety checks rather than an indication that a part has failed.
DIY fix possible
Wait approximately 15 minutes for the program to finishEnsure your external or internal filling loop is closedCheck that the pressure gauge is between 1.0 and 1.5 bar
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Vaillant models that show the P.6 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Vaillant P.6 fault code information on this page is sourced and cross-checked against the official Vaillant service / installation manuals for each affected model.
- Vaillant ecoTEC manual (PDF)
- Vaillant ecoTEC 65kW manual (PDF)
- Vaillant ecoTEC Plus 840 manual (PDF)
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 7 July 2026